A low NOx premix combustion system typically requires the gas-air linkage to maintain a consistent gas-air ratio at different firing rates (2-stage or modulating). Traditionally, a negative regulator type gas valve is applied to provide this control linkage. Such a regulator will be pneumatically coupled to both the air supply and the fuel supply. The mixing chamber will receive the air supply downstream of the regulator coupling and direct the air through flow restrictors (or another component) that lowers the pressure in that portion of the mixing chamber. The fuel supply will enter through an inlet in the portion of the mixing chamber with a lowered pressure. Because the air supply and fuel supply were at equal pressures prior to the flow restrictors, the lowered pressure created by the flow restrictors helps to draw the fuel supply into the mixing chamber. Typically, high negative pressures provide better overall performance, but at a penalty of increased pressure drop.